using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var ringings = new List<Ringing>();

        ringings.Add(new Ringing

        {

            Id = 2,

            Rssi = 1,

            MacAddress = new byte[] { 0x12, 0x34 },

        });

        ringings.Add(new Ringing

        {

            Id = 3,

            Rssi = 2,

            MacAddress = new byte[] { 0x12, 0x34 },

        });

        ringings.Add(new Ringing

        {

            Id = 4,

            Rssi = 4,

            MacAddress = new byte[] { 0x56, 0x78 },

        });

        ringings.Add(new Ringing

        {

            Id = 2,

            Rssi = 10,

            MacAddress = new byte[] { 0x56, 0x78 },

        });

        //group by Id

        Console.WriteLine("Grouped by Id Results:");

        var byId = ringings.GroupBy(x => x.Id).Select(x => x.OrderBy(y => y.Rssi).First());

        foreach (var byIdItem in byId)

            Console.WriteLine(byIdItem.Id + " | " + byIdItem.Rssi + " | " + BitConverter.ToString(byIdItem.MacAddress));

        Console.WriteLine("");

        //group by MacAdress

        Console.WriteLine("Grouped by MacAddress Results:");

        var byMac = ringings.GroupBy(x => BitConverter.ToString(x.MacAddress)).Select(x => x.OrderBy(y => y.Rssi).First());

        foreach (var byMacItem in byMac)

            Console.WriteLine(byMacItem.Id + " | " + byMacItem.Rssi + " | " + BitConverter.ToString(byMacItem.MacAddress));

    }

    protected class Ringing

    {

        public int Id { get; set; }

        public int Rssi { get; set; }

        public byte[] MacAddress { get; set; }

    }

}